from openpyxl import load_workbook

# load_workbook 加载xlsx工作簿到内存中
wb = load_workbook(r"meiri.xlsx");

# sheetnames工作簿sheet名称集合
sheet_names = wb.sheetnames;
for sheet_name in sheet_names:
    ws = wb[sheet_name];
    # 类似map取值
    ws['A4'].value = "装备采购单";
# save（）保存文件
wb.save(r"demo.xlsx");